Abstract

We present evidence to show that changes in the Sun’s equatorial rotation rate are synchronized with changes in its orbital motion about the barycentre of the Solar System. We propose that this synchronization is indicative of a spin–orbit coupling mechanism operating between the Jovian planets and the Sun. However, we are unable to suggest a plausible underlying physical cause for the coupling. Some researchers have proposed that it is the period of the meridional flow in the convective zone of the Sun that controls both the duration and strength of the Solar cycle. We postulate that the overall period of the meridional flow is set by the level of disruption to the flow that is caused by changes in Sun’s equatorial rotation speed. Based on our claim that changes in the Sun’s equatorial rotation rate are synchronized with changes in the Sun’s orbital motion about the barycentre, we propose that the mean period for the Sun’s meridional flow is set by a Synodic resonance between the flow period (~22.3 yr), the overall 178.7-yr repetition period for the solar orbital motion, and the 19.86-yr synodic period of Jupiter and Saturn.

1 In an inferior conjunction, the superior planet (Saturn) is ‘in opposition’ to the Sun, as seen from the inferior planet (Jupiter), and so we will refer to this as Jupiter and Saturn being in opposition.

2 When Jupiter is at superior conjunction as seen from Saturn, we will refer to this as Jupiter and Saturn being in conjunction.

3 World Data Centre for Sunspot Numbers, Belgium.

4 Usoskin & Mursula (2003) claim that there were solar maxima in the years 1720.2 and 1729.0. However, the Wolf Sunspot Numbers for these two cycles appear to peak at 1718.5 and 1727.0. Hence, for these cycles we have used the years for solar maximum quoted by Jose (1965) i.e. 1718.2 and 1727.5.

5 Another interesting point is that the typical change in the Sun’s angular momentum about the CM from one syzygy to the next is ~3 to 5 × 1040 Nms. This is virtually the same as the total rotational angular momentum of the Sun’s convective zone which is ~2 to 3 × 1040 Nms.